Seismic isolation of bridges using variable frequency and variable friction pendulum isolator system

Friction pendulum system (FPS) with spherical sliding surface is an effective isolation system for bridges subjected to earthquake ground motion. However, due to constant curvature, this sliding surface may encounter resonance problem at low frequency. In order to overcome this limitation, an isolation system with variable frequency and variable friction is proposed for bridges in this study. The isolator is similar to typical FPS, but the curvature of the sliding surface and the friction coefficient along the surface are varied and they become a function of sliding displacement. A three-span continuous bridge isolated with variable frequency and variable FPS is analysed to study the effectiveness of the proposed system. It is concluded from the study that the resonance problem due to low frequency ground motion can be prevented using the proposed isolator. The proposed isolator reduces the base shear considerably without increasing the residual displacements. Also, the proposed isolator has the advantages of both the FPS and the pure friction (PF) system.